There are several options for giving your acrylic paintings a final protective coating and a nice even surface.
Acrylic gloss medium will add depth to your colors and give your acrylic painting an oil like appearance. It also provides a protective coating to your finished painting. Diluted to 50%, it can also be used to fix charcoal and pastel. May also be used as a collage adhesive.
Acrylic matte medium does not contain the same hardeners as acrylic gloss medium and should not be used as a final varnish. In addition, matte mediums can cause clouding when used thickly. Acrylic varnish, applied to your finished painting seals the surface and protects against damage and dirt. It can be reversed with mineral spirits.
Acrylic varnish comes in gloss and matte finishes. Gloss varnish leaves a deep shine on the painting, while matte varnish gives a semi-gloss surface. Matte varnish should not be used thickly. For multiple coats, apply gloss on undercoats and apply matte as the final coat.
To apply varnishes, use a soft wide brush and long edge to edge brush strokes. Do not shake the bottle, as that will introduce air bubbles to the liquid. Use thin coats and allow to dry between coats. Do not build layers of matte varnish or medium, as it tends to cloud. Instead, build layers of gloss medium or gloss varnish and finish with a layer of matte.